In general, a gear cutting process includes: forming a gear by machining a predetermined material of the gear by gear cutting; heat-treating the machined gear; and then finishing (grinding) the gear to remove distortion and the like due to this heat treatment. Heretofore, various tooth grinding methods using tools such as white aluminum oxide (WA) grinding wheels and superabrasive (diamond, cubic boron nitride (CBN), and the like) grinding wheels have been provided to efficiently finish the faces of the teeth of a heat-treated gear. Moreover, tools for use in these methods are in external gear form, internal gear form, screw (worm) form, and the like which are chosen in accordance with the form of a gear to be ground.
On the other hand, of gears, internal gears are frequently used in automotive transmissions and the like. Recently, there has been a demand for the improvement of machining accuracy for the purpose of reducing the vibration and noise of such transmissions.
Accordingly, heretofore, an internal gear grinding method has been provided which performs tooth face grinding by synchronously rotating a heat-treated internal gear and a barrel-shaped threaded grinding wheel in mesh with each other with a crossed axes angle therebetween. By such a method, a slip velocity between the internal gear and the threaded grinding wheel is produced using the mesh rotation and the crossed axes angle, and thereby the faces of the teeth of the internal gear can be finely ground. Such a threaded grinding wheel for use in conventional internal gear grinding is disclosed in, for example, Non-Patent Literature 1.